Most Loaches should be in at least a 30 gallon to be comfortable. The Two you picked have the potential to get big. Orange-Finned can reach 8 inches, and Clowns 6-12 easily. Orange-Finned can be aggressive, and Clowns need to be in at least a trio. They do better in numbers above 6 though. Clowns should really be in tanks over 75 Gallons at least. I'm aiming for a 130 to house my 6, and they are only 3 inches now.
Loaches that can live in tanks smaller than 30 gallons include all varieties of kuhlis, and skunk loaches, though skunks are very aggressive at the best of times. Yo yo loaches may work in smaller aquaria, though they can be nippy.
In general loaches are nippy, can be boisterous and can be very secretive, hifding most or all of teh time in the wrong enviroment.
--Mia